1. Field of the Invention
The present invention relates to a patch antenna apparatus for use as a vehicle-mounted small antenna or the like, and more particularly, to beam shaping of the radiation patterns of the patch antenna apparatus.
2. Description of the Related Art
Patch antennas are planar antennas in which a dielectric substrate having a patch electrode on the top surface is disposed on a ground plane and a predetermined high-frequency current is fed to the patch electrode via current-feed pins or the like. The patch antennas are widely used as vehicle-mounted small antennas and the like for receiving satellite waves. In order for the patch antennas to achieve a high gain, the ground plane needs to have a sufficiently large area compared to the patch electrode. Further, for stabilization of the performance of the patch antennas, many patch antennas have a configuration in which an opposing ground electrode is provided on the bottom surface of the dielectric substrate to be in contact with or in close proximity of the ground plane (e.g., Japanese Unexamined Patent Application Publication No. 6-224620, pp. 2–4, FIG. 1).
Typically, since the maximum radiation direction of the patch antennas is directly above the patch electrode, the patch antennas installed on, for example, the roof surfaces of vehicles can efficiently receive signal waves from a satellite located in the vicinity of the zenith.
However, the patch antennas having a maximum radiation direction at the zenith cannot efficiently receive ground waves. Thus, in a system in which a ground-based repeater receives signal waves from a satellite (e.g., an S-band digital audio radio satellite currently being planned) and re-transmits the signal waves, when such a known patch antenna is installed on the roof surface of a vehicle or the like, the antenna cannot be used as a planar antenna for receiving ground waves from the repeater. Consequently, a need arises for an antenna sticking up high, such as a pole antenna. Also, the antennas having the maximum radiation direction at the zenith are not suitable for receiving signal waves from a low elevation-angle satellite.